In modern semiconductor devices, the ever increasing device density and decreasing device dimensions demand more stringent requirements in the packaging or interconnecting techniques of such devices. Conventionally, a flip-chip attachment method has been used in the packaging of IC chips. In the flip-chip attachment method, instead of attaching an IC die to a lead frame in a package, an array of solder balls is formed on the surface of the die.
Injection molded solder (“IMS”) is a technique that dispenses molten solder instead of solder paste. U.S. Pat. No. 5,244,143, which is commonly owned by International Business Machines Corporation, discloses the injection molded solder technique and is hereby incorporated by reference in its entirety. One of the advantages of the IMS technique is that there is very little volume change between the molten solder and the resulting solder bump. The IMS technique utilizes a solder head that fills molds of various materials such as boro-silicate glass, silicon, polymers, metals, and the like that are wide enough to cover most single chip modules. Solder is dispensed into mold cavities as the solder head moves across the mold.
The IMS method for solder bonding is then carried out by applying a molten solder to a substrate in a transfer process. When smaller substrates, i.e., chip scale or single chip modules are encountered, the transfer step is readily accomplished since the solder-filled mold and substrate are relatively small in area and thus can be easily aligned and joined in a number of configurations. For instance, the process of split-optic alignment is frequently used in joining chips to substrates. The same process may also be used to join a chip-scale IMS mold to a substrate (chip) which will be bumped.
A subset technology of IMS is Controlled Collapse Chip Connection New Process (“C4NP. The solder bumps can be inspected in advance and deposited onto the mold in one simple step using this technology. In this technology, a solder head with an injection aperture comprising molten solder scans over the surface of the mold. In order to fill the cavities on the mold, pressure is applied onto the reservoir of the C4NP head which comprises the molten solder as it is scanned over the cavities.
One problem with the current C4NP process is with respect to the fill heads used during the process to place the solder bumps onto molds. Current fill heads comprise a somewhat rigid seal that retains molten solder within the fill head and contacts the mold as the fill head dispenses the solder. However, as the fill head moves across the mold plate the distance between the fill head and the mold plate varies due to the mechanical tolerances of the system. With a somewhat rigid seal this height variation leads to a seal contact force and contact width variation. These variations in seal contact force and width leads to excessive seal wear, poor cavity fill, and can lead to solder leaks in regions of low seal force. Another problem with current C4NP processes is that “round” O-ring seals are utilized within the fill heads. These O-ring seals are prone to rolling in their support groove, which leads to premature seal failure.
Therefore a need exists to overcome the problems with the prior art as discussed above.